This invention relates to a rear hub for a bicycle, and more particularly to a rear hub for a bicycle, which has two or more sprockets of different diameters among which a driving chain is switched for changing the bicycle speed.
Generally, a rear hub for a bicycle comprises a hub shaft, a hub shell supported rotatably to the hub shaft through a pair of bearings, and a driving member having two or more sprockets of different diameters which are supported at one axial end of the hub shell to be freely rotatable in one direction through a unidirectional rotary transmission. A back fork of the bicycle is sandwiched at each leg between a lock nut screwed with the hub shaft to fix the bearing and a tightening nut screwed with the axially outermost end of hub shaft, so that the tightening nut is tightened to fix the hub shaft to the back fork.
A high speed sprocket having the least number of teeth of all the sprockets, faces a leg of the back fork providing an interval between it and the leg nearly equal to or larger than width of the driving chain. Accordingly, the driving chain, when switched from a low speed sprocket having a larger number of teeth to the high speed sprocket may disengage from the high speed sprocket and enter and jam in this interval.
A protector has been provided axially outwardly of the high speed sprocket in order to prevent disengagement of the chain therefrom, the protector being fixed to the driving member and rotatable together therewith.
In this construction, the protector contacts with the back fork due to its mounting condition. Therefore, the driving member is conventionally axially shifted toward the center of the axial length of the hub shaft, so that the outermost sprocket at the driving member may be spaced from the back fork by a given interval.
When the driving member is shifted in this manner, the hub flange carrying spokes of a wheel which is positioned at one axial end of the hub shell, at the driving member side, is also shifted toward the center of axial length of the hub shaft. As a result, the center of axial length of the wheel and that of axial length between the one hub flange and the other opposite thereto, are considerably axially offset thus increasing the so-called offset amount, thereby reducing the strength of the wheel. Also, the rotatable protector may catch a foreign object within a space existing between the protector and the back fork.
The above problem is solved by fixing the protector to the back fork, using any suitable fixing means. However, another problem then occurs in that a protector of proper size cannot be readily selected correspondingly to different sized sprockets when a bicycle is assembled. In other words, the protector should be fixed to the back fork prior to assembly of the bicycle, so that if and when the sprocket size is changed, the already fixed protector can easily be replaced by a new one corresponding to the changed sprocket.
This invention has been designed in order to overcome the above problems. An object of the invention is to provide a rear hub for a bicycle, which can simply mount the protector with respect to the high speed sprocket without an increase of the offset amount and which permits easily selection of the proper protector size corresponding to the diameter of the high speed sprocket.
The present invention is directed to supporting the protector by use of the fixing member fixed to the hub shaft, such as a lock nut or the like. The invention was devised after careful observation of the fact that, in a bicycle rear hub, bearings for rotatably supporting the hub shell are fixed to the hub shaft through fixing members, such as tightening nuts and lock nuts, the fixing members contacting with the back fork to thereby fix the hub shaft thereto, and that the fixing member, such as the lock nut, is positioned axially outwardly from one end of the driving member.
This invention is characterized in that the rear bicycle hub, which supports the hub shell rotatably to the hub shaft through a pair of bearings and carries at one axial end of the hub shell two or more sprockets supported to be freely rotatably in one direction, is provided with a protector arranged axially outwardly of the smallest diameter high speed sprocket the protector being larger in diameter than the high speed sprocket. The protector is supported to a fixing member fixed to the hub shaft.
The fixing member mainly comprises a lock nut screwed with the hub shaft for fixing the bearing to the hub shaft. The protector is fit onto the lock nut through a bore which is formed at the center of the protector and has a size and shape corresponding to the external size and shape of the lock nut. The protector is prevented from axial movement by being tightly is fit onto the lock nut, or the protector is formed of a material, e.g., a synthetic resin, which is elastically deformable and not harder than the lock nut and is elastically press-fit thereto. Alternatively, the protector is formed with a thick center and is sandwiched between the back fork and a sealing member supported to the lock nut, the bearing or a tightening nut therefor.
Accordingly, the hub of the invention utilizes the fixing member for easily mounting the protector, thereby avoiding an increase in the offset amount and renders a particular fixing means unnecessary. In addition, a protector of proper size corresponding to the diameter of the high speed sprocket can be readily selected.
These and other objects and novel features of the invention will be more apparent from the following description which is provided in conjunction with the accompanying drawings.